a. Field of the Invention
This invention relates to an arrangement of speakers for a low-frequency sound reproduction system particularly adopted for high power output. More particularly, the invention is directed to a manifold for coupling multiple low frequency loudspeakers, in a single sound-radiating enclosure.
b. Description of the Prior Art
Multiple loudspeakers are often used in sound applications requiring high acoustic power output (sound volume), such as in theaters or arenas, or for studio and stage monitoring, discotheques and the like. In many sound systems, several components, such as driver/horn assemblies or cone/enclosure loudspeakers, are used for sound reproduction across the entire range of audible sound, with different devices covering the bass (low-frequency), midrange and high-frequency portions of the sound spectrum. Low-frequency speakers are customarily referred to as "woofers".
A particular sound application may require an especially high power output across the whole audio spectrum. With respect to the low-frequency range, this has been accomplished in the past, in general, by increasing the number of loudspeakers, because of the need to set large volumes of air in motion to create high acoustic power. In order to move large air volumes, the excursion of a moving diaphragm having a given cone area could be increased, but since acoustic distortion increases with increasing excursion once the linear limitation of the loudspeaker suspension is reached, the solution of using multiple loudspeakers is generally preferred.
Multiple loudspeakers are conventionally mounted on a front baffle board of a speaker housing or enclosure. The housing may be closed, or may be provided with one or more phase-inverting ports or ducts (as in a bass-reflex type enclosure). Acoustic coupling and addition occurs in such structures at frequencies where the wavelengths are sufficiently greater than the distances between the individual speakers or phase-inverting ports.
U.S. Pat. Nos. 4,391,346 and 4,437,540 issued to Murakami et al. respectively on July 5, 1983 and March 20, 1984, show another approach to combining the outputs of several speaker units. The individual speaker units are set in the walls of a cavity behind a front baffle board. The speaker units of Murakami et al. are arranged so that the sound-radiating axis of each speaker unit angularly converges on and is concentrated on a point of the central axis of the cavity, just behind the front baffle, toward which the speakers are generally aimed. While such an arrangement may improve mid-range sound reproduction, low-end frequency reproduction is adversely affected, as the cavity behaves like a short acoustic horn having a rapid flare rate, such a horn being incapable of sustaining very low-frequency sounds.
This invention is directed to solving these drawbacks by providing a novel and unique loudspeaker manifolding system.